This invention relates to techniques and devices for mixing heterogeneous gas specimens to obtain homogeneous blends. More specifically, it relates to methods and means for mixing breath specimens for medical analysis, which specimens are introduced into the devices of the invention directly by exhalation from the individual being tested.
The use of mixing chambers for obtaining breath specimens of patients for medical analysis is know. For example, in analyzing or treating respiratory ailments, or simply for performing diagnostic or metabolism tests, it is often desirable to obtain a full breath sample from a patient and to analyze the sample for, e.g., carbon dioxide content. Ideally, the analytical device is connected directly to a breath receiving apparatus, so that as the patient exhales, his breath specimen passes into the analytical device for immediate monitoring and analysis. However, the composition of an individual's breath is nonuniform, in that the initial exhalation delivers a gaseous composition containing an amount of carbon dioxide which differs from that contained at the end of an exhalation. This results in variable results in the analytical determinations, depending upon just what portion of a particular exhaled volume of breath is sampled by the analytical equipment.
It has been contemplated to take an entire exhalation volume of breath and thoroughly mix it before analyzing it or sampling it for analysis. Typically, patients exhaled into a collapsible bag, and then after the breath specimen was maintained in the bag long enough to ensure thorough mixing, a sample of the contents was removed and analyzed. Other devices have used large baffled boxes in which mixing was attempted by forcing a breath specimen to pass through the box and around a system of baffles designed to enhance the mixing of all the breath constituents. Still other devices relied upon using a motor and fan to thoroughly mix a breath specimen before analysis.
Each of the prior art techniques suffered from one or more deficiencies. Some produced a high back pressure, so that when the patient attempted to exhale into the mixing device, the pressure built up, especially at high flow rates, making it difficult, uncomfortable, or inefficient for the patient to exhale to the maximum extent. This problem was aggravated in the case of individuals having respiratory ailments or in the case of small children with inadequate capacity to exhale against high back pressures.
Other prior art devices were slow to use or resulted in uncertainties as to their mixing efficiency, so that it was not feasible to use them in a continuous manner such that a patient could exhale repeatedly directly through the mixing device into the analytical equipment.
Prior art devices have also been generally difficult to clean, so that contamination between consecutive users was a risk. Also, some devices of the prior art were devised for use with an average size of breath specimen and were not amenable to ready adjustment for differences in the size of breath specimen between small children and adults.
The problems and deficiencies of the prior art can be overcome or greatly alleviated in accordance with the present invention